View - ResearchSpace@Auckland - The University of Auckland

Figure 7.1 1: Exhaled No determined at single breath plateau concentrations at increasing expiratory
flows and at increasing expiratory mouth pressures
E r.o
Ci 15.0
2 ; 10.0
6
E s.o
ril o.o
r 1.5
o
'".
-E t.o
O'1""'O"'O"''
I
15
l0
5
0
1.5
?? I T I
+-f "'1""?"'1'.0
II--
o
U
x
o 0.5
z 051015n
Arway presswo, cmHP
T t "la-...+..o]..{
T '.--.1
, J{""'t"'i
fr^
5o 10 150 200 250 s
grytmryflownF, mLrl
Taken from Hogman M, Stromberg s, schedin Frostell c, Hedenstierna G, Gustafsson LE' Nitric oxide
from the human r"rpit'"tow tract-efficiently quantified by standarized single bl99!h measurements'
n.i" iny"iologica Sclndinavia 1997; 159: i+S'Sae (Hogman, Stromberg et al' 1997)'
In the pressure experiment, there were no significant differences between the mean exhaled
NO concentrations at 4mmHg, 8mmHg, l2mmHg and 16mmHg' In Figure 7 '3 it can be seen
that most of the ten subjects appeared to have flat traces across the sets of exhalation but the
top two and the bottom one subjects' traces do appear to have a reduction in No with the
increased pressure settings. There was a trend towards differences between the peak COz
levels reached being 5.907o at 4mmHg, 5.837o at 8mmHg, 5'83Vo at l2mmHg and 5'53Vo
reached at 16mmHg. This is likely to be accounted for by there also being differences in the
duration of exhalation with 49.9s at 4mmHg, 49.6s at 8mmHg ,44.2s at l2mmHg and 40'9s at
16mmHg. The differences probably reflect the difficulty for subjects of maintaining
exhalation against a strong resistance at constant flow to generate the higher mouth pressures'
subjects found it tiring to maintain this pressure and found it difficult to keep their lips tight
around the mouthpiece so as not to allow any air to escape when exhaling' When designing
the experiment in the preliminary trials both myself and Carolyn Busst tried a range of
expiratory mouth pressures up to 2OmmHg, and we quickly dropped this last high pressure as
being extremely difficult to exhale against. Two other studies published at the same time
showed no difference in the NO with differing pressures. In five subjects there was no
difference between an expiratory pressure of 6mmHg and 2ommHg (Silkoff 1997 ' Marked
flow dependence). And in six subjects at expiratory pressures over 0 to 20cmHzO there was
no difference in exhaled NO (see Figure 7.9 above, Hogman)' It would appear that mouth
173